23,214 research outputs found
Recent developments in Vorton Theory
This article provides a concise overview of recent theoretical results
concerning the theory of vortons, which are defined to be (centrifugally
supported) equilibrium configurations of (current carrying) cosmic string
loops. Following a presentation of the results of work on the dynamical
evolution of small circular string loops, whose minimum energy states are the
simplest examples of vortons, recent order of magnitude estimates of the
cosmological density of vortons produced in various kinds of theoretical
scenario are briefly summarised.Comment: 6 pages Latex. Contribution to 1996 Cosmology Meeting, Peyresq,
Franc
ERTS-1 image contributes to understanding of geologic structures related to Managua earthquake, 1972
ERTS-1 imaged the western portion of Nicaragua on December 24, 1972, one day after the central part of the city of Managua was devastated by a major earthquake which measured 5.6 on the Richter scale. ERTS-1 images reveal sets of lineaments (which may reflect fault systems) along any one of which movement could have taken place. One set includes a line of active volcanoes that parallels the coast and constitutes the southwestern edge of the Nicaraguan Depression, a regional graben which cuts obliquely across the Central American isthmus. This trend is offset approximately 10km in a right lateral geometric sense just west of the city of Managua. A parallel lineament, north of Lake Managua, marks the northeast edge of the graben. A second set, extends northward to northwestward from the mouth of the Rio Grande (Viejo) north of Lake Managua and can be projected southward across the lake to Managua. It is this set along which geometric offset of the volcanic lineament appears to have taken place
New concept in brazing metallic honeycomb panels
Aluminum oxide coating provides surface which will not be wetted by brazing alloy and which stops metallic diffusion welding of tooling materials to part being produced. This method eliminates loss of tooling materials and parts from braze wetting and allows fall-apart disassembly of tooling after brazing
Involution products in Coxeter groups
For W a Coxeter group, let
= {w â W | w = xy where x, y â W and x 2 = 1 = y 2}.
It is well known that if W is finite then W = . Suppose that w â . Then the minimum value of â(x) + â(y) â â(w), where x, y â W with w = xy and x 2 = 1 = y 2, is called the excess of w (â is the length function of W). The main result established here is that w is always W-conjugate to an element with excess equal to zero
Staticity Theorem for Higher Dimensional Generalized Einstein-Maxwell System
We derive formulas for variations of mass, angular momentum and canonical
energy in Einstein (n-2)-gauge form field theory by means of the ADM formalism.
Considering the initial data for the manifold with an interior boundary which
has the topology of (n-2)-sphere we obtained the generalized first law of black
hole thermodynamics. Supposing that a black hole evevt horizon comprisesw a
bifurcation Killing horizon with a bifurcate surface we find that the solution
is static in the exterior world, when the Killing timelike vector field is
normal to the horizon and has vanishing electric or magnetic fields on static
slices.Comment: 10 pages, REVTEX, to published in Phys.Rev. D1
Transonic Elastic Model for Wiggly Goto-Nambu String
The hitherto controversial proposition that a ``wiggly" Goto-Nambu cosmic
string can be effectively represented by an elastic string model of exactly
transonic type (with energy density inversely proportional to its tension
) is shown to have a firm mathematical basis.Comment: 8 pages, plain TeX, no figure
Dynamical Stability of Witten Rings
The dynamical stability of cosmic rings, or vortons, is investigated for the
particular equation of state given by the Witten bosonic model. It is found
that there exists a finite range of the state parameter for which the vorton
states are actually stable against dynamical perturbations. Inclusion of the
electromagnetic self action into the equation of state slightly shrinks the
stability region but otherwise yields no qualitative difference. If the Witten
bosonic model represents a good approximation for more realistic string models,
then the cosmological vorton excess problem can only be solved by assuming
either that strings are formed at low energy scales or that some quantum
instability may develop at a sufficient rate.Comment: 11 pages, LaTeX-ReVTeX (v.3), 2 figures available upon request, DAMTP
R-94/1
Renormalisation of gravitational self interaction for wiggly strings
It is shown that for any elastic string model with energy density and
tension , the divergent contribution from gravitational self interaction can
be allowed for by an action renormalisation proportional to . This
formula is applied to the important special case of a bare model of the
transonic type (characterised by a constant value of the product ) that
represents the macroscopically averaged effect of shortwavelength wiggles on an
underlying microscopic model of the Nambu-Goto type (characterised by ).Comment: 11 pages, Latex; original 8 page version extended to include
estimates of relevant orders of magnitude. To be published in Physical
Review,
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